EP0431766A1 - Improved attachment of a gas turbine engine blade to a turbine rotor disc - Google Patents

Improved attachment of a gas turbine engine blade to a turbine rotor disc Download PDF

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Publication number
EP0431766A1
EP0431766A1 EP90312336A EP90312336A EP0431766A1 EP 0431766 A1 EP0431766 A1 EP 0431766A1 EP 90312336 A EP90312336 A EP 90312336A EP 90312336 A EP90312336 A EP 90312336A EP 0431766 A1 EP0431766 A1 EP 0431766A1
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EP
European Patent Office
Prior art keywords
tooth
root
flank
disc
attachment
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP90312336A
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German (de)
French (fr)
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EP0431766B1 (en
Inventor
Neil Milner Evans
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rolls Royce PLC
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Rolls Royce PLC
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Publication date
Application filed by Rolls Royce PLC filed Critical Rolls Royce PLC
Publication of EP0431766A1 publication Critical patent/EP0431766A1/en
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Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/30—Fixing blades to rotors; Blade roots ; Blade spacers
    • F01D5/3007—Fixing blades to rotors; Blade roots ; Blade spacers of axial insertion type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2250/00—Geometry
    • F05D2250/70—Shape
    • F05D2250/71—Shape curved
    • F05D2250/711—Shape curved convex
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Definitions

  • This invention relates to an improved attachment of a gas turbine engine blade to a turbine rotor disc.
  • the aerofoil blades of a gas turbine engine both in the compressors and the turbines, usually extend radially from a disc or drum or similar rotor structure.
  • the engagement between the blades and the supporting rotor disc is a most important part of the design of any such bladed rotor; it must sustain the loads carried from the blade to the rotor without failure, and it must be overall as small as possible in order to reduce the size of the blade root and disc rim to a minimum.
  • root attachments have been proposed and used. These have usually been of a general type in which the root has projections which engage with undercut surfaces of a corresponding slot or groove in the periphery of the rotor disc.
  • the slots may extend between opposed faces of the disc, or may extend circumferentially of the disc periphery.
  • One widely used member of the former class is called a "firtree" root attachment, after the approximate resemblance of the cross-section of the blade provided to a fir tree.
  • firtree root is described and illustrated in our British Patent 2030657B.
  • the present invention is particularly concerned with firtree root attachments.
  • the problem of increased stressing of the root teeth due to increased performance requirements may be overcome by reducing the number of teeth per root from 4 to 2, for example, and by reducing the tooth aspect ratio accordingly.
  • the tooth aspect ratio is the ratio of the perpendicular distance between the apex of a tooth and an adjacent trough and the width of the tooth between adjacent troughs.
  • the present invention seeks to alleviate undesirable load distributions in a firtree root tooth by providing localized contact only between a flank of the tooth and an adjacent undercut surface of a corresponding slot in the rotor disc to which the root is attached.
  • a root attachment for a blade of a gas turbine engine comprising a firtree root on the blade which has at least one tooth adapted to engage with a notch within a shaped slot formed in the disc to which the blade is attached, characterized in that an undercut surface of the notch adjacent a flank of a said at least one tooth is substantially planar and the flank has a convex curvature having a maximum elevation relative to a straight line drawn between the tip of the tooth and the base of an adjacent trough, whereby initial contact between the undercut surface and the flank under zero loading is solely at the location of said maximum elevation and under increased loading the flank crushes at said location to provide an area of load-spreading contact around said location.
  • the location of the maximum elevation is at a point providing an optimum balance between root and disc notch stresses, which point may be at or near the mid-point of the tooth flank.
  • the firtree root comprises at least two opposed pairs of teeth.
  • only one flank of a tooth being the radially outer flank of the tooth with respect to the axis of the disc, is convexedly curved, the other flank being substantially planar.
  • FIG. 1 there is shown an aircraft gas turbine engine comprising a casing 10, within which are mounted a compressor 11, a combustion chamber 12, a turbine 13 and a final nozzle 14. Operation of the engine overall is conventional and is therefore not described herein.
  • the casing 10 is shown cut away in the vicinity of the turbine 13 to expose to view the turbine rotor disc 15 and its associated rotor blades 16.
  • the blades 16 are not integral with the rotor disc 15 but are held in axially extending (but not parallel with the disc axis) slots or grooves 17 by the engagement therein of correspondingly shaped roots 18.
  • the blades 16 are mounted in an angularly spaced apart circumferential row on the disc 15.
  • Figure 2 shows in enlargement a cross-section through the mid-section of one of the blades 16 and the associated area of disc 15, the plane of the section being perpendicular to the disc axis. Shown in section are the aerofoil 19, the platform 20, the root shank 21, and the root 18 itself.
  • the root 18, as shown, is provided with six teeth 22 disposed in two opposed plane arrays 23, 24 of three teeth each, symmetrically disposed about the central plane 25 of the blade.
  • Each tooth 22 is located in a respective notch 26 extending perpendicularly to the central plane 25.
  • Each notch 26 is of a shape corresponding generally to the shape of the tooth 22 located in it, the undercut surface 27 of the notch, that is, the surface nearest the radially outer surface of the disc, being planar in its extent from the trough of the notch to the peak between that notch and the next.
  • the profile of each notch 26 is not identical to that of the corresponding tooth 22.
  • the teeth 22 have a longitudinal extent equal to that of the entire root; that is, they extend into and out of the plane of the paper in the orientation of Figure 2.
  • the shape of the teeth remains constant throughout their longitudinal extent and the further enlarged view of Figure 3 enables this shape to be understood more easily. It should be understood that all the teeth have the same general profile so that although only one tooth is described with reference to Figure 3, all the other teeth will in fact be similar.
  • the radially outermost flank 28 of tooth 22 is convexedly curved so that it contacts the opposed undercut surface 27 of the notch 26 at a contact point 29 of that surface.
  • This curvature of the tooth flank is herein termed "barrelling".
  • the barrelling of the flank 28 is chosen so that it reaches a maximum elevation relative to a straight line drawn between the tip of the tooth and the base of an adjacent trough at a point 30 which is chosen as that point of the tooth which provides an optimum balance between blade root and disc notch stresses when subjected to load, and which corresponds to the point of contact 29 with the notch surface 27.
  • This point 30 will usually be at or near the centre of the tooth flank.
  • a number of chain lines drawn in Figure 3 show the dimensions of the tooth 22 and the distortions taking place when it is under load against the undercut surface of the notch 26. Accordingly, “a” is the width of the tooth 22 across its base between adjacent troughs, and “b” is the height of the tooth, and, as mentioned above, the ratio b/a is the aspect ratio of the tooth, “h” is the barrel height of the tooth flank 28, “d” is the maximum depth of surface deformation of the barrelling under load, “L(tot)” is the bearing surface contact width, “L(el)” is that portion of the bearing surface subject to elastic deformation only, and “L(el + pl)” is that portion of the bearing surface subject to a combination of plastic and elastic deformation.
  • the point 30 of maximum elevation of the curvature of the tooth flank need not coincide with the centre point of the tooth flank if it is desired to move the balance between the various stresses towards the position of peak blade stress in the trough between two teeth, or towards the position of peak disc stress, which is in the trough of a disc notch.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)

Abstract

In a gas turbine firtree root tooth (22) structure in which a firtree root (21) is retained in a shaped slot in a turbine rotor disc (15) by means of teeth (22) cooperating with notches (26) in the slot, the bearing surface (28) of a root tooth (22) is barrelled against a planar surface (27) of the respective notch (26) so as to give point contact (29) against that surface, whereby, under load, the barrelled surface (28) crushes so as to override pitch tolerances and even out load distribution. If the barrelling is located at or in the vicinity of the tooth face centre, the tendency of the tooth to crack under repeated loadings is minimized.

Description

  • This invention relates to an improved attachment of a gas turbine engine blade to a turbine rotor disc.
  • As is well known in the art, the aerofoil blades of a gas turbine engine, both in the compressors and the turbines, usually extend radially from a disc or drum or similar rotor structure. The engagement between the blades and the supporting rotor disc is a most important part of the design of any such bladed rotor; it must sustain the loads carried from the blade to the rotor without failure, and it must be overall as small as possible in order to reduce the size of the blade root and disc rim to a minimum.
  • In the past, a variety of root attachments have been proposed and used. These have usually been of a general type in which the root has projections which engage with undercut surfaces of a corresponding slot or groove in the periphery of the rotor disc. The slots may extend between opposed faces of the disc, or may extend circumferentially of the disc periphery. One widely used member of the former class is called a "firtree" root attachment, after the approximate resemblance of the cross-section of the blade provided to a fir tree. One such firtree root is described and illustrated in our British Patent 2030657B. The present invention is particularly concerned with firtree root attachments.
  • The increased performance demanded of gas turbine engines in modern aircraft, especially in those of the military genre, imposes very high loads on the turbine blades and correspondingly high loads on the teeth of the firtree root attachments.
  • After several hundred hours of high performance loading it is possible for a serration crack to appear in the firtree root. Of the estimated serration stress more than half may be due to tooth bending. In a high performance high pressure turbine up to 50% of the total load carried by the turbine disc will be incorporated in the blade firtree and its associated disc firtree. For turbines designed for even higher performance this percentage of total load carried by the disc will increase even more.
  • The problem of increased stressing of the root teeth due to increased performance requirements may be overcome by reducing the number of teeth per root from 4 to 2, for example, and by reducing the tooth aspect ratio accordingly. The tooth aspect ratio is the ratio of the perpendicular distance between the apex of a tooth and an adjacent trough and the width of the tooth between adjacent troughs.
  • Reduction of the tooth aspect ratio results in a stiffer tooth and lower bending stresses. However, this beneficial effect can raise a further problem in that the load distribution between pairs of teeth radially disposed is made worse due to the reduced tooth deflections being less able to accomodate the radial tolerances between adjacent pairs of teeth. It is an object of the present invention to alleviate this problem.
  • Accordingly, in general terms the present invention seeks to alleviate undesirable load distributions in a firtree root tooth by providing localized contact only between a flank of the tooth and an adjacent undercut surface of a corresponding slot in the rotor disc to which the root is attached.
  • In particular, there may be provided a root attachment for a blade of a gas turbine engine, the attachment comprising a firtree root on the blade which has at least one tooth adapted to engage with a notch within a shaped slot formed in the disc to which the blade is attached, characterized in that an undercut surface of the notch adjacent a flank of a said at least one tooth is substantially planar and the flank has a convex curvature having a maximum elevation relative to a straight line drawn between the tip of the tooth and the base of an adjacent trough, whereby initial contact between the undercut surface and the flank under zero loading is solely at the location of said maximum elevation and under increased loading the flank crushes at said location to provide an area of load-spreading contact around said location.
  • Preferably, the location of the maximum elevation is at a point providing an optimum balance between root and disc notch stresses, which point may be at or near the mid-point of the tooth flank.
  • Preferably, the firtree root comprises at least two opposed pairs of teeth.
  • Preferably, only one flank of a tooth, being the radially outer flank of the tooth with respect to the axis of the disc, is convexedly curved, the other flank being substantially planar.
  • The invention will now be described by way of example only with reference to the accompanying diagrammatic non-scale drawings in which:
    • Figure 1 is a partly cut away view of an aircraft gas turbine engine having a root attachment in accordance with the invention,
    • Figure 2 is an enlarged section through a blade and root portion of the engine of Figure 1 and in accordance with the invention, and
    • Figure 3 is a further enlargement of portion III of the section of Figure 2, showing further detail of the invention.
  • In Figure 1 there is shown an aircraft gas turbine engine comprising a casing 10, within which are mounted a compressor 11, a combustion chamber 12, a turbine 13 and a final nozzle 14. Operation of the engine overall is conventional and is therefore not described herein.
  • The casing 10 is shown cut away in the vicinity of the turbine 13 to expose to view the turbine rotor disc 15 and its associated rotor blades 16. As is usual in gas turbines, the blades 16 are not integral with the rotor disc 15 but are held in axially extending (but not parallel with the disc axis) slots or grooves 17 by the engagement therein of correspondingly shaped roots 18. The blades 16 are mounted in an angularly spaced apart circumferential row on the disc 15.
  • Figure 2 shows in enlargement a cross-section through the mid-section of one of the blades 16 and the associated area of disc 15, the plane of the section being perpendicular to the disc axis. Shown in section are the aerofoil 19, the platform 20, the root shank 21, and the root 18 itself. The root 18, as shown, is provided with six teeth 22 disposed in two opposed plane arrays 23, 24 of three teeth each, symmetrically disposed about the central plane 25 of the blade.
  • Each tooth 22 is located in a respective notch 26 extending perpendicularly to the central plane 25. Each notch 26 is of a shape corresponding generally to the shape of the tooth 22 located in it, the undercut surface 27 of the notch, that is, the surface nearest the radially outer surface of the disc, being planar in its extent from the trough of the notch to the peak between that notch and the next. However, as will be described below, the profile of each notch 26 is not identical to that of the corresponding tooth 22.
  • It will be appreciated that the teeth 22 have a longitudinal extent equal to that of the entire root; that is, they extend into and out of the plane of the paper in the orientation of Figure 2. However, the shape of the teeth remains constant throughout their longitudinal extent and the further enlarged view of Figure 3 enables this shape to be understood more easily. It should be understood that all the teeth have the same general profile so that although only one tooth is described with reference to Figure 3, all the other teeth will in fact be similar.
  • As is shown in Figure 3, the radially outermost flank 28 of tooth 22 is convexedly curved so that it contacts the opposed undercut surface 27 of the notch 26 at a contact point 29 of that surface. This curvature of the tooth flank is herein termed "barrelling". The barrelling of the flank 28 is chosen so that it reaches a maximum elevation relative to a straight line drawn between the tip of the tooth and the base of an adjacent trough at a point 30 which is chosen as that point of the tooth which provides an optimum balance between blade root and disc notch stresses when subjected to load, and which corresponds to the point of contact 29 with the notch surface 27. This point 30 will usually be at or near the centre of the tooth flank.
  • The effect of the barrelling of the tooth flank 28 against the planar undercut surface 27 of the notch 26 is that under load the bearing surface of the tooth will crush and spread out in area around the point 30 so as to override pitch tolerance and even out load distributions and thereby minimize the onset of cracking.
  • A number of chain lines drawn in Figure 3 show the dimensions of the tooth 22 and the distortions taking place when it is under load against the undercut surface of the notch 26. Accordingly, "a" is the width of the tooth 22 across its base between adjacent troughs, and "b" is the height of the tooth, and, as mentioned above, the ratio b/a is the aspect ratio of the tooth, "h" is the barrel height of the tooth flank 28, "d" is the maximum depth of surface deformation of the barrelling under load, "L(tot)" is the bearing surface contact width, "L(el)" is that portion of the bearing surface subject to elastic deformation only, and "L(el + pl)" is that portion of the bearing surface subject to a combination of plastic and elastic deformation.
  • Although three pairs of teeth 22 are illustrated, it will be understood that in other embodiments of the invention fewer or more than three pairs of teeth may be used without departing from the scope of the invention. Further, in some embodiments, the point 30 of maximum elevation of the curvature of the tooth flank need not coincide with the centre point of the tooth flank if it is desired to move the balance between the various stresses towards the position of peak blade stress in the trough between two teeth, or towards the position of peak disc stress, which is in the trough of a disc notch.

Claims (5)

  1. In a gas turbine engine having a plurality of aerofoil blades (16) attached to a rotor disc (15), a root attachment for a said blade, the attachment comprising a firtree root (18) on the blade (16) which has at least one tooth (22) adapted to engage with a notch (26) within a shaped slot (17) formed in the disc (15) to which the blade (16) is attached, characterised in that an undercut surface (27) of the notch (26) adjacent a flank (28) of a said at least one tooth (22) is substantially planar and the flank (28) has a convex curvature having a maximum elevation relative to a straight line drawn between the tip of the tooth (22) and the base of an adjacent trough, whereby initial contact between the undercut surface (27) and the flank (28) under zero loading is solely at the location of said maximum elevation and under increased loading the flank (28) crushes at said location to provide an area of load-spreading contact around said location.
  2. A root attachment as claimed in claim 1 wherein the location of the maximum elevation is at a point providing an optimum balance between the root and disc notch stresses.
  3. A root attachment as claimed in claim 2 wherein the point is at or near the mid-point of the tooth flank (28).
  4. A root attachment as claimed in claim 1 wherein the firtree root (18) comprises at least two opposed pairs of teeth (22).
  5. A root attachment as claimed in claim 1 wherein only one flank (28) of a tooth (22), being the radially outer flank of the tooth with respect to the axis of the rotor, is convexedly curved, the other flank being substantially planar.
EP90312336A 1989-11-30 1990-11-12 Improved attachment of a gas turbine engine blade to a turbine rotor disc Expired - Lifetime EP0431766B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8927096 1989-11-30
GB8927096A GB2238581B (en) 1989-11-30 1989-11-30 Improved attachment of a gas turbine engine blade to a turbine rotor disc

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Publication Number Publication Date
EP0431766A1 true EP0431766A1 (en) 1991-06-12
EP0431766B1 EP0431766B1 (en) 1996-02-21

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US (1) US5110262A (en)
EP (1) EP0431766B1 (en)
JP (1) JPH03182603A (en)
DE (1) DE69025456T2 (en)
GB (1) GB2238581B (en)

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ES2070720A2 (en) * 1992-03-24 1995-06-01 Westinghouse Electric Corp Two-lug side-entry turbine blade attachment
EP0799972A1 (en) * 1996-04-02 1997-10-08 ROLLS-ROYCE plc A root attachment for a Turbomachine blade
WO1999042703A1 (en) * 1998-02-23 1999-08-26 Alliedsignal Inc. Turbine blade attachment stress reduction rings
EP1584792A1 (en) * 2004-04-08 2005-10-12 Siemens Aktiengesellschaft Blade attachment for a compressor or a turbine
EP2546465A1 (en) 2011-07-14 2013-01-16 Siemens Aktiengesellschaft Blade root, corresponding blade, rotor disc, and turbomachine assembly
EP2998516A1 (en) * 2014-09-18 2016-03-23 Rolls-Royce plc Gas turbine engine
US9359905B2 (en) 2012-02-27 2016-06-07 Solar Turbines Incorporated Turbine engine rotor blade groove
EP3045664A1 (en) * 2015-01-16 2016-07-20 Siemens Aktiengesellschaft Rotor blade fixing for a thermal flow engine
EP3425162A1 (en) * 2017-07-07 2019-01-09 Siemens Aktiengesellschaft Turbine blade and fixing recess for a flow engine, and producing method thereof

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US8047796B2 (en) * 2007-11-16 2011-11-01 General Electric Company Dovetail attachment for use with turbine assemblies and methods of assembling turbine assemblies
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US10895160B1 (en) 2017-04-07 2021-01-19 Glenn B. Sinclair Stress relief via unblended edge radii in blade attachments in gas turbines
DE102019219403A1 (en) * 2019-12-12 2021-06-17 MTU Aero Engines AG Rotor for a turbo machine and turbo machine
CN113623019B (en) * 2020-05-09 2023-09-15 中国石化工程建设有限公司 Flue gas turbine moving blade assembly and flue gas turbine
DE102021120876A1 (en) * 2021-08-11 2023-02-16 MTU Aero Engines AG BLADE BASE HOLDER TO ACCEPT A BLADE
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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2070720A2 (en) * 1992-03-24 1995-06-01 Westinghouse Electric Corp Two-lug side-entry turbine blade attachment
EP0799972A1 (en) * 1996-04-02 1997-10-08 ROLLS-ROYCE plc A root attachment for a Turbomachine blade
WO1999042703A1 (en) * 1998-02-23 1999-08-26 Alliedsignal Inc. Turbine blade attachment stress reduction rings
EP1584792A1 (en) * 2004-04-08 2005-10-12 Siemens Aktiengesellschaft Blade attachment for a compressor or a turbine
WO2005098204A1 (en) * 2004-04-08 2005-10-20 Siemens Aktiengesellschaft Blade fixing system for a compressor or a turbine
WO2013007587A1 (en) 2011-07-14 2013-01-17 Siemens Aktiengesellschaft Blade root, corresponding blade, rotor disc, and turbomachine assembly
EP2546465A1 (en) 2011-07-14 2013-01-16 Siemens Aktiengesellschaft Blade root, corresponding blade, rotor disc, and turbomachine assembly
RU2612675C2 (en) * 2011-07-14 2017-03-13 Сименс Акциенгезелльшафт Blade root, corresponding blade, rotor disc and turbomachine unit
US9359905B2 (en) 2012-02-27 2016-06-07 Solar Turbines Incorporated Turbine engine rotor blade groove
EP2998516A1 (en) * 2014-09-18 2016-03-23 Rolls-Royce plc Gas turbine engine
US9841031B2 (en) 2014-09-18 2017-12-12 Rolls-Royce Plc Gas turbine engine
EP3045664A1 (en) * 2015-01-16 2016-07-20 Siemens Aktiengesellschaft Rotor blade fixing for a thermal flow engine
EP3425162A1 (en) * 2017-07-07 2019-01-09 Siemens Aktiengesellschaft Turbine blade and fixing recess for a flow engine, and producing method thereof

Also Published As

Publication number Publication date
GB2238581A (en) 1991-06-05
GB2238581B (en) 1994-01-12
DE69025456D1 (en) 1996-03-28
US5110262A (en) 1992-05-05
EP0431766B1 (en) 1996-02-21
GB8927096D0 (en) 1990-01-31
DE69025456T2 (en) 1996-08-01
JPH03182603A (en) 1991-08-08

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